Natural gas is often produced far away from the sites where it is intended to be used. A method used for transporting it consists in liquefying the natural gas around −160° C. and in transporting it by ship in liquid form at atmospheric pressure.
Prior to being liquefied, the natural gas has to undergo various treatments in order, on the one hand, to adjust its composition with a view to sale (sulfur and carbon dioxide content, calorific value) and, on the other hand, to allow liquefaction thereof. In particular, natural gas fractionation carried out by distillation allows to remove the heavier hydrocarbons likely to clog, through crystallization, the lines and the heat exchangers of the liquefaction plant. Furthermore, fractionation by distillation allows to separately recover compounds such as ethane, propane or butane that can be upgraded separately, for example for sale or as cooling fluids used in the liquefaction process.
Liquefaction is generally carried out at a pressure approximately equal to the operating pressure of the fractionating column.
The present invention aims to modify the fractionation stage by increasing the fractionation operating pressure and, consequently, by increasing the pressure at which the natural gas is liquefied so as to improve the overall efficiency of the liquefaction method.